L-type calcium channel blockers like verapamil are used in the
prophylaxis of migraine. However, their effect on the expression of CGRP in the
trigeminal nucleus caudalis (TNC) is unknown. It is important because an
earlier study had shown that olcegepant, a CGRP receptor antagonist, acts at
the level of the trigeminal spinal nucleus rather than the trigeminal ganglia.
Nimodipine was used in the present study as it crosses the blood-brain barrier.
The objective of the study was to determine the pattern of expression of
calcitonin gene-related peptide (CGRP) in the TNC after administration of
nimodipine and/or morphine. Wistar rats were injected with saline, morphine,
nimodipine or morphine + nimodipine for
14 days. Subsequently, the lowest part of the medulla oblongata containing the
spinal nucleus was removed and processed for immunohistochemical localization
of CGRP. The density of expression was quantified using Image J software.
The results were statistically analyzed. CGRP expression was noted over the
superficial part of the TNC, which decreased significantly after nimodipine
administration. Conversely, morphine produced an up-regulation. The expression
was unchanged with reference to saline in the morphine + nimodipine treated group.
Decreased expression of CGRP in the trigeminal nucleus caudalis after
nimodipine is being reported for the first time. Also, whether CGRP expression
can be used as a marker for predicting the therapeutic efficacy of an
anti-migraine drug is currently being investigated.